Thales inspired the Milesian school of philosophy and was followed by Anaximander, who argued that the substratum or arche could not be water or any of the classical elements but was instead something "unlimited" or "indefinite" (in Greek, the apeiron). He began from the observation that the world seems to consist of opposites (e.g., hot and cold), yet a thing can become its opposite (e.g., a hot thing cold).

610 BC) was a pre-Socratic Greek philosopher who lived in Miletus, a city of Ionia (in modern-day Turkey).

It dealt with a wide variety of subjects, including political philosophy, ethics, metaphysics, ontology, logic, biology, rhetoric and aesthetics. At least twenty-nine of his treatises have survived, known as the corpus Aristotelicum, and address a variety of subjects including logic, physics, optics, metaphysics, ethics, rhetoric, politics, poetry, botany, and zoology.

Socrates (469–399 BC) was one of the first Greek philosophers to encourage both scholars and the common citizen to turn their attention from the outside world to the condition of humankind.

Pythagoreanism also incorporated ascetic ideals, emphasizing purgation, metempsychosis, and consequently a respect for all animal life; much was made of the correspondence between mathematics and the cosmos in a musical harmony.

Generally, the term is derived from the context of ancient Greek philosophy, and has been recontextualised by modern philosophers such as Arthur Schopenhauer and Kurt Gödel; otherwise, the term "transmigration" is more appropriate.

Thales inspired the Milesian school of philosophy and was followed by Anaximander, who argued that the substratum or arche could not be water or any of the classical elements but was instead something "unlimited" or "indefinite" (in Greek, the apeiron). He began from the observation that the world seems to consist of opposites (e.g., hot and cold), yet a thing can become its opposite (e.g., a hot thing cold).

The apeiron is central to the cosmological theory created by Anaximander, a 6th-century BC pre-Socratic Greek philosopher whose work is mostly lost.

Thales inspired the Milesian school of philosophy and was followed by Anaximander, who argued that the substratum or arche could not be water or any of the classical elements but was instead something "unlimited" or "indefinite" (in Greek, the apeiron). He began from the observation that the world seems to consist of opposites (e.g., hot and cold), yet a thing can become its opposite (e.g., a hot thing cold). Contrary to the Milesian school, which posits one stable element as the arche, Heraclitus taught that panta rhei ("everything flows"), the closest element to this eternal flux being fire.

In ancient Greek philosophy, Aristotle foregrounded the meaning of arche as the element or principle of a thing, which although undemonstrable and intangible in itself, provides the conditions of the possibility of that thing.

This initial state is ageless and imperishable, and everything returns to it according to necessity Anaximenes in turn held that the arche was air, although John Burnet argues that by this he meant that it was a transparent mist, the aether. Despite their varied answers, the Milesian school was searching for a natural substance that would remain unchanged despite appearing in different forms, and thus represents one of the first scientific attempts to answer the question that would lead to the development of modern atomic theory; "the Milesians," says Burnet, "asked for the φύσις of all things."

The term is central to Greek philosophy, and as a consequence to Western philosophy as a whole.

The power of Parmenides' logic was such that some subsequent philosophers abandoned the monism of the Milesians, Xenophanes, Heraclitus, and Parmenides, where one thing was the arche, and adopted pluralism, such as Empedocles and Anaxagoras.

Prodicus, Gorgias, Hippias, and Thrasymachus appear in various dialogues, sometimes explicitly teaching that while nature provides no ethical guidance, the guidance that the laws provide is worthless, or that nature favors those who act against the laws.

Prodicus of Ceos (, Pródikos ho Keios; c. 465 BC – c. 395 BC) was a Greek philosopher, and part of the first generation of Sophists.

Prodicus, Gorgias, Hippias, and Thrasymachus appear in various dialogues, sometimes explicitly teaching that while nature provides no ethical guidance, the guidance that the laws provide is worthless, or that nature favors those who act against the laws. Subsequent philosophic tradition was so influenced by Socrates as presented by Plato that it is conventional to refer to philosophy developed prior to Socrates as pre-Socratic philosophy.

Unlike nearly all of his philosophical contemporaries, Plato's entire work is believed to have survived intact for over 2,400 years.

While philosophy was an established pursuit prior to Socrates, Cicero credits him as "the first who brought philosophy down from the heavens, placed it in cities, introduced it into families, and obliged it to examine into life and morals, and good and evil."

Cicero introduced the Romans to the chief schools of Greek philosophy and created a Latin philosophical vocabulary (with neologisms such as evidentia, humanitas, qualitas, quantitas, and essentia) distinguishing himself as a translator and philosopher.

Many philosophers around the world agree that Greek philosophy has influenced much of Western culture since its inception.

The separation of philosophy and science from theology began in Greece during the 6th century BC. Thales, an astronomer and mathematician, was considered by Aristotle to be the first philosopher of the Greek tradition.

It holds that non-material abstract (but substantial) forms (or ideas), and not the material world of change known to us through our physical senses, possess the highest and most fundamental kind of reality.

Ousia is a philosophical and theological term, originally used in Ancient Greek philosophy, and also in Christian theology.

Aristotle's fame was not great during the Hellenistic period, when Stoic logic was in vogue, but later peripatetic commentators popularized his work, which eventually contributed heavily to Islamic, Jewish, and medieval Christian philosophy.

This initial state is ageless and imperishable, and everything returns to it according to necessity Anaximenes in turn held that the arche was air, although John Burnet argues that by this he meant that it was a transparent mist, the aether. Despite their varied answers, the Milesian school was searching for a natural substance that would remain unchanged despite appearing in different forms, and thus represents one of the first scientific attempts to answer the question that would lead to the development of modern atomic theory; "the Milesians," says Burnet, "asked for the φύσις of all things."

However, in his Book On the Heavens he introduced a new "first" element to the system of the classical elements of Ionian philosophy.

Clear, unbroken lines of influence lead from ancient Greek and Hellenistic philosophers to Early Islamic philosophy, the European Renaissance and the Age of Enlightenment. The spread of Christianity throughout the Roman world, followed by the spread of Islam, ushered in the end of Hellenistic philosophy and the beginnings of Medieval philosophy, which was dominated by the three Abrahamic traditions: Jewish philosophy, Christian philosophy, and early Islamic philosophy.

Islamic law placed importance on formulating standards of argument, which gave rise to a novel approach to logic in Kalam, but this approach was later displaced by ideas from Greek philosophy and Hellenistic philosophy with the rise of the Mu'tazili philosophers, who highly valued Aristotle's Organon.

The spread of Christianity throughout the Roman world, followed by the spread of Islam, ushered in the end of Hellenistic philosophy and the beginnings of Medieval philosophy, which was dominated by the three Abrahamic traditions: Jewish philosophy, Christian philosophy, and early Islamic philosophy.

Medieval re-discovery of ancient Greek philosophy among the Geonim of 10th century Babylonian academies brought rationalist philosophy into Biblical-Talmudic Judaism.

At least twenty-nine of his treatises have survived, known as the corpus Aristotelicum, and address a variety of subjects including logic, physics, optics, metaphysics, ethics, rhetoric, politics, poetry, botany, and zoology.

These practical developments were followed by the development of theories of light and vision by ancient Greek and Indian philosophers, and the development of geometrical optics in the Greco-Roman world.

Proclus Lycaeus (8 February 412 – 17 April 485 AD), called the Successor (Greek Πρόκλος ὁ Διάδοχος, Próklos ho Diádokhos), was a Greek Neoplatonist philosopher, one of the last major classical philosophers (see Damascius).